From 76b90efa8f53feb4bf844ad4454b1290fa1cdb3a Mon Sep 17 00:00:00 2001
From: LI Qing <geding.lq@alibaba-inc.com>
Date: Thu, 13 Feb 2020 04:02:43 +0000
Subject: [PATCH] Fix read_at() in SEFS if offset beyond the end of the file

---
 src/libos/src/fs/sefs/sgx_storage.rs | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/libos/src/fs/sefs/sgx_storage.rs b/src/libos/src/fs/sefs/sgx_storage.rs
index 8b024bb0..c872c74f 100644
--- a/src/libos/src/fs/sefs/sgx_storage.rs
+++ b/src/libos/src/fs/sefs/sgx_storage.rs
@@ -172,6 +172,14 @@ impl File for LockedFile {
             return Ok(0);
         }
         let mut file = self.0.lock().unwrap();
+
+        // SgxFile does not support to seek a position beyond the end.
+        // So check if file_size < offset and return zero(indicates end of file).
+        let file_size = file.seek(SeekFrom::End(0)).expect("failed to tell SgxFile") as usize;
+        if file_size < offset {
+            return Ok(0);
+        }
+
         let offset = offset as u64;
         file.seek(SeekFrom::Start(offset))
             .expect("failed to seek SgxFile");
@@ -185,8 +193,8 @@ impl File for LockedFile {
         }
         let mut file = self.0.lock().unwrap();
 
-        // SgxFile do not support seek a position after the end.
-        // So check the size and padding zeros if necessary.
+        // SgxFile does not support to seek a position beyond the end.
+        // So check if file_size < offset and padding null bytes.
         let file_size = file.seek(SeekFrom::End(0)).expect("failed to tell SgxFile") as usize;
         if file_size < offset {
             static ZEROS: [u8; 0x1000] = [0; 0x1000];